Motor-driven hand-held machine tool

ABSTRACT

A motor-driven hand-held machine tool with spindle brake, in particular an angle grinder (1), has a device for clamping a disk-shaped tool (33, 83) at a work spindle (7, 67) between an inner flange (29, 79) and an outer flange (31, 81) which has a central bore hole (39, 84) overlapping the work spindle (7, 67) with play. The outer flange (31, 81) can be screwed on a fastening thread (37, 85) against the working rotational direction of the work spindle (7, 67). The hand-held machine tool is designed in such a way that the clamping pressure on the tool (63, 83) between the inner and outer flange (29, 31, 79, 81) can be increased when the work spindle (7, 67) is braked and the tool (33, 83) continues to rotate because of the inertia resulting from the braking so that the tool (33, 63) cannot be loosened from the work spindle (7, 67) unintentionally when the latter is braked.

PRIOR ART

The invention concerns a motor-driven hand-held machine tool accordingto the generic part of claim 1.

A hand-held machine tool of the generic type is known from U.S. Pat. No.4,735,020. Its work spindle can be stopped or braked by a spindle stopdevice and the screwing moment can then be applied by the drive motorfor loosening the fastening nut for the grinding tool. The fastening nutmay be loosened from the work spindle entirely by hand.

The known hand-held machine tool has the disadvantage that when the workspindle is suddenly stopped after turning off the motor by actuating thespindle stop device, the grinding disk tends to continue rotating as aresult of its inertia and, in so doing, to loosen itself and theclamping device from the work spindle.

This unintentional loosening of the clamping device can cause thegrinding disk to disengage from the work spindle at high speeds andendanger the operator or bystanders as a result of its high inherentenergy.

ADVANTAGES OF THE INVENTION

In contrast to the prior art, the hand-held machine tool according tothe invention with the characterizing features of claim 1 has theadvantage that an unintentional loosening of the disk-shaped tool, inparticular the grinding disk, is prevented also when actuating thespindle stop device at high speeds of the work spindle. This results ina great increase in safety.

Further advantageous constructions of the invention result from thedependent claims.

DRAWING

Embodiment examples of the invention are explained in more detail in thefollowing description with reference to the accompanying drawing.

FIG. 1 shows a hand-held machine tool in a first embodiment example ofthe invention;

FIG. 2 shows a detail of a second embodiment example of the invention;and

FIG. 3 is another view of the second embodiment example according toFIG. 2.

DESCRIPTION OF THE EMBODIMENT EXAMPLES

The angle grinder 1 shown in FIG. 1 in a sectional view as seen from thefront has a motor housing 3 and a gear unit housing 5. A work spindle 7with a lathed or turned collar 9 is held in a bearing 11 in the gearunit housing 5. Axially adjacent thereto, a stepped sleeve 13 carrying acollar 15 at its upper end is shrunk on to the work spindle 7. On itsside remote of the collar 15, the stepped sleeve 13 is arranged in anadditional bearing 17 so as to be rotatable, but secured against fallingout.

The sleeve 13 supports a bevel gear 19 on its collar 15 in such a waythat it is fixed with respect to rotation relative thereto. A spindlestop device 21 arranged in the gear unit housing 5 is associated withthe bevel gear 19. The spindle stop device 21 substantially has apressure pin 25 which is supported so as to be axially displaceableagainst a spring 23 and can lock into recesses 27 on the outercircumference of the bevel gear 19. By catching in these recesses, itcan stop the bevel gear 19 and accordingly the work spindle 7.

A grinding disk 33 is clamped on the free end of the work spindle 7between an inner flange 29 and an outer flange 31. The inner flange 29with its bore hole is arranged so as to be rotatable in a defined mannerand, on the side of the work spindle 7 remote of the free end, so as tobe displaceable axially in a defined manner as far as the collar 35. Theouter flange 31 fits on an external thread 37 on the free end of thework spindle 7, the external thread 37 having a slope angle. Thegrinding disk 33 has a central recess 39 by which it overlaps the workspindle 7 with play. On its side remote of the grinding disk 33, theinner flange 29 carries a gear-like wedge body 41 with an axial wedgeface 43 which slopes upward toward the right as seen in the viewingdirection at an angle and is supported at an axial counter-wedge face 45of an approximately U-shaped recess 47 in the end face 49 of the sleeve13, which axial counter-wedge face 45 slopes upward in the samedirection. The lateral defining walls 51, 53 of the U-shaped recess 47act as radial stops. The U-shaped recess 47 has roughly twice the widthof the wedge body 41. When the inner flange 29 is rotated relative tothe work spindle 7, the latter is displaced axially by the wedge effectof the wedge faces 43, 45 sliding on one another. Therefore, by rotatingthe inner flange 29 toward the left as seen in the viewing direction,the clamping pressure on the grinding disk 33 is increased.

The rotating direction of the work spindle 7 is designated by an arrow55 facing toward the left. The pitch or slope 57 of the thread 37 atangle is less than the slope 59 of the wedge face 43 and counter-wedgeface 45 at angle.

When the work spindle 7 is braked suddenly, the grinding disk 33 has atendency to continue rotating in the original direction due to its massinertia. In so doing, it tries to turn the outer flange 31 and the innerflange 29 on the work spindle 7. Since the thread 37 is a right-handedthread, a rotation of the grinding disk 33 toward the left causes aloosening moment at the screw connection between the outer flange 31 andthe work spindle 7. However, this loosening moment is at least balancedor compensated for by the axial displacement of the inner flange 29 bythe sliding of the wedge face 43 on the counter-wedge face 45. Inaddition, the width of the recess 47 is so dimensioned that the wedgebody 41 does not contact the radial stop 51 in the U-shaped recess 47even in the event of an extremely high loosening moment caused by themass inertia of the grinding disk 33, since this would prevent furtheraxial displacement of the inner flange 29 and an unintentional looseningof the grinding disk 33 would be possible.

When screwing on the outer flange 31 for clamping the grinding disk 33,the smallest possible distance between the inner flange 29 and the endside 49 of the sleeve 13 is always produced by rotation in theright-hand direction, i.e. the wedge faces 43, 45 are supported one ontop of the other. Thus, the wedge body 41 constantly contacts theright-hand defining wall 53 of the U-shaped recess 47 in the clampedstate. In this way it is ensured that there will be a sufficientpossibility of radial rotation for the inner flange 29 if the spindlestop device 21 is suddenly actuated so that the inner flange 29 canincrease the clamping pressure on the grinding disk 33 and accordinglyon the outer flange 31 and secures the screwing connection of the outerflange 31 in the manner of a profile nut.

The additional embodiment example of the invention which is shownschematically in FIG. 2 has a work spindle 67 on which are screwed aninner flange 79 and an outer flange 81, a grinding disk 83 being clampedbetween the latter. The grinding disk 83 is provided with a centralrecess 84 which surrounds the work spindle 67 concentrically with play.The outer flange 81 fits on an external thread 85 having a smallpitch--angle of slope--on the free end of the work spindle 67. The innerflange 79 fits on an external thread 87--angle of slope--having agreater inclination to the work spindle 67 which is separated from theexternal thread 85 by a notch 88.

A projecting stop 89 which projects out axially in the manner of a gearis arranged on the side of the inner flange 79 remote of the grindingdisk 83. The stop 89 overlaps a rod-like stop 91 which passes throughthe work spindle 67 parallel to its diameter and is held therein. Thestops 89, 91 accordingly define the rotating possibility and, at thesame time, the axial movement of the inner flange 87. The distancebetween the stops 89, 91 is so dimensioned that even in the event of anextremely high loosening moment due to the mass inertia of the tool 83the continued rotation of the grinding disk 83 does not result in thestops 89, 91 contacting one another because this would prevent furtheraxial displacement of the inner flange 87 and an unintentional looseningof the grinding disk 83 would be possible.

FIG. 3 shows the embodiment example of FIG. 2 in a position rotated by90° around the axis of the work spindle to illustrate the arrangement ofthe inner flange 79 and its stop 89 relative to the stop 91. The secondembodiment example operates fundamentally in the same way as shown inFIG. 1, the difference being that the thread 87 according to FIGS. 2 and3 causes the inner flange 79 to be displaced axially when the latter isrotated, whereas in the embodiment example of FIG. 1 this is effected bythe wedge face. If the work spindle 67 is suddenly braked, the grindingdisk 83 tries to rotate the inner flange 79 and the outer flange 81 onthe work spindle 87 in the loosening direction of the outer flange 81.The clamping pressure on the grinding disk 83 is increased in that theinner flange 79 is axially displaced faster than the outer flange 81when rotated. Accordingly, the loosening moment at the outer flange 81is not exceeded and the screw connection between the outer flange 81 andthe thread 85 remains stable. An unintentional loosening of thisconnection is impossible even under extreme conditions so that there isno risk of injury to the operator or bystanders in such cases.Accordingly, a safety device for hand-held machine tools withdisk-shaped tools is provided in a simple manner.

In an embodiment example of the invention which is not shown in thedrawing, the inner flange is fastened on the work spindle so as to befixed with respect to rotation and axial displacement relative thereto.The outer flange supports a flange disk which is rotatable in a definedmanner so as to abut against wedge faces, the clamping pressure beingtransmitted to the grinding disk by means of this flange disk. Thedistance between the flange disk and the outer flange changes when theflange disk is rotated relative to the outer flange. The clampingpressure on the grinding disk is accordingly increased from the side ofthe outer flange when braking the work spindle.

In the solution according to U.S. Pat. No. 4,735,020, as well as in allother hand-held grinding machine tools with clamping nuts which may betightened manually, there is a risk that when the spindle comes to anabrupt stop in a design according to the invention the clamping nut willbe tightened in such a way that it can only be loosened with anauxiliary tool. For this reason, an important criterion in the use ofthe invention consists in that the axial displacement of the outer orinner flange is defined.

There is no risk of an excessive clamping torque in the event of anabrupt braking of the spindle when using the invention when a clampingscrew according to DE-OS 37 05 638 or DE-OS 38 41 181 is employed.

I claim:
 1. A motor-driven hand-held machine tool, comprising a workspindle; a spindle brake; a disc-shaped tool having a central bore holeand surrounding said work spindle with said central bore hole with play;an inner flange and an outer flange between which said disc-shaped toolis clamped; said work spindle being provided with a fastening thread,said outer flange being screwable on said fastening thread against aworking rotational direction of said work spindle, said inner and outerflanges and said working spindle being formed so that during braking ofsaid working spindle when said disc-shaped tool continues rotating inthe working rotational direction due to its mass inertia, a clampingpressure between said tool and said inner and outer flanges is increasedautomatically.
 2. A motor-driven hand-held machine tool as defined inclaim 1, wherein said inner and outer flanges and said working spindleare formed so that the clamping pressure on the tool is increased duringbraking of said working spindle by said spindle brake.
 3. A motor-drivenhand-held machine tool as defined in claim 1, wherein said inner andouter flanges and said working spindle are formed so that the clampingpressure on the tool is increased during braking of said working spindleby action of a turned-off motor.
 4. A motor-driven hand-held machinetool as defined in claim 1, wherein said inner and outer flanges areformed so that an axial displacement of one of said flanges on said workspindle relative to said disc-shaped tool results from a relativerotation with reference to said work spindle in the working rotationaldirection.
 5. A motor-driven hand-held machine tool as defined in claim4; and further comprising wedge means, said inner flange being displacedaxially in that it is coupled with said wedge means which, when rotatingfurther in the working rotational direction jointly with saiddisc-shaped tool, are rotated along by said disc-shaped tool, slideagainst one another, and attempt to reduce an axial distance between oneof said inner flange and said disc-shaped tool,and said inner flange andsaid outer flange.
 6. A motor-driven hand-held machine tool as definedin claim 5, wherein said wedge means are formed so that when rotatingfurther in the working rotational direction jointly with saiddisc-shaped tool they are rotated along by said disc-shaped tool bymeans of axial contact pressure.
 7. A motor-driven hand-held machinetool as defined in claim 5, wherein said wedge means are formed so thatwhen rotating further in the working rotational direction jointly withsaid disc-shaped tool they are rotated along by said disc-shaped tool bymeans of a positive-locking engagement.
 8. A motor-driven hand-heldmachine tool as defined in claim 5, wherein said wedge means have wedgesurfaces having a slope angle, said inner flange being rotatable in adefined manner in the same screwing direction as said outer flange onsaid wedge faces.
 9. A motor-driven hand-held machine tool as defined inclaim 12; and further comprising radial stops which define arotatability of said inner flange relative to said work spindle.
 10. Amotor-driven hand-held machine tool as defined in claim 1; and furthercomprising means for increasing a clamping pressure and arranged in saidouter flange.
 11. A motor-driven hand-held machine tool as defined inclaim 1, wherein said inner flange is arranged so as to be fixed withrespect to rotation relative to said work spindle, said outer flangesupporting axial displaceable cams facing said tool so that an axialdisplacement of said cams in direction of said tool in reaching aclamping position is minimal and a maximum is reached when said toolcontinues to rotate relative to said work spindle as a result of inertiaby means of rotational driving.
 12. A motor-driven hand-held machinetool, comprising a work spindle; a spindle brake; a disc-shaped toolhaving a central bore hole and surrounding said work spindle with saidcentral bore hole with play; an inner flange and an outer flange betweenwhich said disc-shaped tool is clamped; said work spindle being providedwith a fastening thread, said outer flange being screwable on saidfastening thread against a working rotational direction of said workspindle, said inner and outer flanges and said working spindle beingformed so that during braking of said working spindle wherein saiddisc-shaped tool continues rotating in the working rotational directiondue to its mass inertia, a clamping pressure between said tool and saidinner and outer flanges is increased automatically; and said workspindle being provided with a further thread having a steeper angle ofinclination than said fastening thread, said inner flange beingrotatable on said further thread in a same screwing direction as saidouter flange.
 13. A motor-driven hand-held machine tool as defined inclaim 12; and further comprising radial stops which define arotatability of said inner flange relative to said work spindle.